vin, a, 2 Reibling: Portland Cement 121 



in the recommendations for improving the present specifications 

 which were given in a previous paper. 8 



PROPOSED BONUS SYSTEM 



In view of the foregoing, I suggest that Portland cement be 

 purchased as heretofore from the lowest bidder who guarantees 

 to fulfill the requirement of specifications, and that the following 

 provisions be made for bonuses to be awarded for superior 

 quality : ^ 



1. No bonus will be awarded unless the cement passes all of 

 the specified requirements including perfect soundness after the 

 steaming test and unless the cement is reasonably uniform in 

 quality and suitably packed. 



2. A bonus of 10 centavos per barrel will be awarded if the 

 specific gravity is consistently above 3.10 (or the loss by ignition 

 not greater than 2 per cent) . 



3. A bonus of 10 centavos per barrel will be awarded if the 

 residue on the number 200 sieve is less than 15 per cent, and 

 that on the number 100 sieve less than 3 per cent. 



4. Provided the gravity is not less than 3.10 (or the loss by 

 ignition not greater than 2 per cent), a bonus of 10 centavos 

 per barrel will be awarded if the 28-day, 1 : 3, standard Ottawa- 

 sand briquettes show consistently an average tensile strength 

 above 400 pounds per square inch. 9 



The above would provide bonuses for superior mixing, grind- 

 ing, and burning, and would permit the manufacturer to earn 

 30 centavos (15 cents United States currency) per barrel in 

 excess of the selling price. In Manila, 30 centavos is about 5.7 

 per cent of the usual cost of Portland cement and less than 1 

 per cent of the cost of concrete. On the other hand, such a 

 system properly enforced ought to secure at least 10 per cent 

 better concrete, eliminate the necessity of rejecting cement, and 

 secure greater certainty in its use. 



Owing to the varying influences of local conditions in different 

 localities on the cost of manufacture, the values given in this 

 proposed system are not arbitrary. However, the principles 

 constitute the essential features, and they must remain fixed. 



"This Journal, Sec. A (1912), 7, 189-191; also, Met. & Chem. Eng. 

 Special number (Sept., 1912), 10, 612; Eng. News (1913), 69, 298, and 

 Cem. & Eng. News (1913), 25, 91. 



* The above recommendations provide for the possibility of a well-burned 

 cement with a lower specific gravity than 3.10, if the low gravity is not due 

 to an absorption of volatile constituent, but our experience does not include 

 such a possibility. 



